Increasing concern about supply shut-off possibilities, steady increase in crude petroleum prices, lack of local indigenous petroleum resources, and desire to become energy independent has resulted in an increased interest in the exploration of alternative fuels which can be used in place of or as a supplement to the fuels currently available, such as gasoline and diesel fuel.
This increased interest in alternative fuels has resulted in experimental uses of such alternative diesel fuels as coal liquids and vegetable oils, and, in some isolated cases, some internal combustion engines have even been operated on solid fuels. This interest has also generated research in the area of fuel additives to increase engine output over that obtainable with heretofore known fuel-air mixtures.
However, at the present time, it appears that alcohols have produced the best results when used as an alternative fuel or as a substitute. Even though the use of alcohol as an automotive fuel has been known for a long time, and ethanol blended with gasoline has been used in locations where it is plentiful a a by-product of sugar refining, pulp manufacture or some similar industry, the use of alcohol in diesel engines as a complete or partial substitution of diesel fuel has been investigated with increasing intensity in the last five to ten years.
Both ethanol and methanol have been looked upon favorably for their ability to produce power and reduce smoke emissions by partial substitution, and alcohols are now seen as potential candidates to reduce diesel fuel consumption in case of emergency or in their own merit as effective alternate fuels.
There are various experimental methods known for using alcohol in diesel engines. These include surface ignition, alcohol with cetane improvers, fumigation, dual injection, and emulsification. The first two methods require engine operation with alcohol alone as fuel. The other three techniques need some amount of diesel fuel to start ignition and/or to control combustion. The techniques differ in the way alcohol is introduced into the engine, thus: alcohol is introduced with the intake air in the fumigation technique; dual-fuel injection employs two separate injection systems, one for alcohol and the other for diesel fuel; and with emulsification, alcohol and diesel fuel are injected into the combustion chamber as a prepared emulsion.
Each of these techniques requires specific modifications to adapt the necessary equipment to the engine, and thus each has certain problems; e.g., fuel system compatibility with alcohol or physical space in the cylinder head for a second injector. Fumigation, however, requires less major modifications than any of the above mentioned techniques, and offers a potential for a retrofit kit for power units in case of fuel emergency. Engines modified for fumigation can also be easily readapted to run on diesel fuel alone.
Fumigation, as used herein, is a process where a part of the fuel in a diesel engine is supplied by alcohol through engine air intake. The remaining diesel fuel is delivered normally by a high-pressure injection system into the engine cylinder. The energy released from alcohol addition reduces the diesel fuel consumption, and thus fumigation presents a relatively easy method to burn lower proof alcohol without requiring major engine modifications.
Diesel spray ignition permits leaner alcohol/air mixture combustion than is usually attainable by spark ignition, therefore, in this respect, fumigation resembles certain types of stratified charge operations where an over-lean premixed charge is ignited by a rich burning jet.
A number of fumigation systems have been investigated prior to recent interest in alcohol fuels. Then, an important objective was to achieve increased smoke-limited power. These fumigation systems are briefly discussed below.
In-line heated vaporizer PA1 Auxiliary mist generator PA1 Carburetor PA1 Direct Manifold Injection PA1 Alcohol Injection System Control
The vaporizer consists of a heated metal container in the intake air supply line. Liquid alcohol evaporates when dropped on the container bottom and then mixes with an intake air stream. Some alcohol droplets can also be carried by the air stream. The heating of the container results in a penalty of higher intake air temperature, reducing volumetric efficiency.
A "micro-fog" of alcohol mist (droplet size less than 4 microns) produced by a mist generator is used to convey alcohol to the air intake manifold.
A conventional carburetor is employed to supply an alcohol/air mixture to the engine. However, with this method of fumigation, it is necessary to throttle a pair of the air flow to ensure adequate air supply through the carburetor, and this may present problems. the carburetor can also be preceded by a heat exchanger to transfer heat from the exhaust gas to the intake air.
This method of fumigation has been used in some recent experiments, and has been proposed as a method for an engine retrofit kit. In this arrangement, alcohol is injected directly into the intake manifold. The injection is possible at a number of positions; e.g., upstream of a turbocharger, downstream of the compressor, before or after the aftercooler and immediately upstream of individual inlet ports. In the last case several injectors are required, one for each cylinder. The location and arrangement of spray nozzles strongly influence engine performance, and thus may present design and performance problems.
The orientation of nozzles relative to the intake air stream has noticeable effects; e.g., injecting alcohol against the air flow increases the relative velocity many times compared with parallel flow and thus significantly increases the vaporization, and high intake air velocities may be required to aerodynamically shatter and vaporize the injected alcohol, therefore presenting more potential design and performance problems.
For turbocharged engines, high-pressure injection equipment can be used to inject a fine spray of alcohol ahead of the turbocharger, but this is an expensive arrangement. A less costly arrangement is to use air from the compressor to introduce liquid alcohol ahead of the turbocharger. This method, however, has been reported to damage the compressor wheel of the turbocharger as a result of droplets impacting this high speed component.
This system is similar to a diesel injection system. Manifold injection of alcohol, continuous or pulsed, can be controlled by mechanical or electronic and hydraulic means, and alcohol flow rates must be controlled for various speeds and loads to optimize diesel fuel replacement. However, this system may become complex and expensive.
Thus, there are drawbacks to each of the above-discussed known fumigation systems.
As discussed above, fumigation is an effective way to efficiently utilize alcohol as an alternative fuel or as an additive. To achieve the fullest possible benefits of fumigation, a fumigation configuration and schedule in a diesel engine should produce the highest possible alcohol substitution with the best thermal efficiency possible.
Presently known fumigation systems for diesel engines do not appear to account for all of the factors pertinent to efficient fumigation, and therefore do not perform as efficiently and as reliably as possible and therefore do not appear to achieve the fullest possible benefits for fumigation.
Thus, while alcohol as a fuel has long been recognized, see, e.g., M. Retel, "Utilization of Alcohol as Motor Fuel by Director Injection," The Engineer's Digest, December 1945, pages 598-602, and fuel additives have been used in spark ignition engines by devices such as is disclosed in U.S. Pat. No. 2,616,404 which injects fluid into a carburetor based on carburetor air flow, such devices and disclosures do not appear to be concerned with means and methods of fumigation.
This shortcoming is overcome by disclosures such as Brille, et al, U.S. Pat. No. 3,665,905 and M. Alperstein, et al, "Fumigation Kills Smoke, Improves Diesel Performance," Trans. SAE 66, 574 (1958) which are directed to fumigation per se. However, Alperstein used an in-line heated vaporizer, an auxiliary mist generator, a carburetor and pneumatic manifold injection for fumigation and found large performance variations, and Brille et al injection fuel upstream of the inlet of a pump which is then subjected to possible damage.
The device disclosed by Gosslau in U.S. Pat. No. 2,369,665 injects fuel into the casing of an air blower to be mixed with air injested into that blower so a mixture in a gaseous state is moved to an engine inlet, and thus appears to avoid problems associated with fuel injection upstream of the inlet of such air blowers. However, this patent does not appear to discuss problems associated with fumigation in a diesel engine, nor does this patent appear to approach problems associated with injecting fuel in accordance with the amount of a primary fuel injected as the device disclosed in Gosslau injects only one fuel, and controls the amount of this fuel injected according to air inlet pressure only.
Thus, there is need for a means for efficiently carrying out fumigation in a diesel engine.
In addition to requiring proper placement of the apparatus associated with a fumigation system, such a system should account for the quantity of alcohol fuel injection whereby the alcohol is utilized in an efficient manner. The above-discussed considerations are pertinent to developing an alcohol injection schedule which makes efficient use of fumigation.
While it is known in the spark ignition field to inject auxiliary fluids during high power operation, see Hans, U.S. Pat. No. 2,129,930, or according to carburetor air flow, see U.S. Pat. No. 4,380,974, such disclosures may not account for all of the considerations involved in fumigation of diesel engines.
Spakowski, in U.S. Pat. No. 4,376,433, discloses a supplemental fuel injection system for incorporating supplemental fuel into the air or air-fuel mixture flowing through a carburetor. This system overcomes some of the deficiencies discussed above by accounting for various engine operating parameters such as engine load and throttle position, such a system appears to be intended for use with spark ignition type engines and supplies only one fuel at a time to the engine and thus still does not appear to account for all of the problems and considerations necessary to design an efficient fumigation system for a diesel engine.
The Spakowski patent also discloses use of a micro-computer to control flow in the supplemental fuel injection system, and patents such as Grosso, U.S. Pat. No. 4,380,974 and Concepcion, U.S. Pat. No. 4,342,287 disclose mechanical linkages to control flow of fluid in a supplemental fuel system. However, these devices do not appear to be adequate to fully account for a proper secondary fuel utilization schedule which will perform efficient fumigation in a diesel engine.